The present invention relates to a laser power control system and related method, and more particularly, to a laser power control system and related method for reducing a settling time in a target laser power transition.
In an optical disc drive, such as a digital versatile disc (DVD) recorder, a laser diode of an optical pick-up unit (OPU) is commonly used as the source of light for reading digital data from and writing digital data to an optical disc. When the read/write state changes, an output laser power of the optical pick-up unit should be changed accordingly. In general, the output laser power of the optical pick-up unit depends on a working temperature of the optical pick-up unit, which means that the output laser power of the optical pick-up unit changes slightly over different working temperatures. Therefore, a feedback control circuit (i.e. a closed loop system) having a low bandwidth is adopted in order to control the laser power of the optical pick-up unit. As is well known in the art, this kind of feedback control circuit is known as an automatic power control (APC) system. Since the APC system has a low bandwidth, changing the control effort in response to the state change fails to make the output laser power change to a target level quickly. For example, when the read/write state changes, it will take significant time to make the output laser power of the optical pick-up unit reach the target power. Therefore, for a closed loop system having a low bandwidth, a novel mechanism is required to reduce the transition time between a current output level and a next output level when a control effort is made due to the state change.